This invention relates to methods of polishing surfaces using magnetorheological fluids.
Workpieces such as glass optical lenses, semiconductors, tubes, and ceramics have been polished in the art using one-piece polishing tools made of resin, rubber, polyurethane or other solid materials. The working surface of the polishing tool should conform to the workpiece surface. This makes polishing complex surfaces complicated, and difficult to adapt to large-scale production. Additionally, heat transfer from such a solid polishing tool is generally poor, and can result in superheated and deformed workpieces and polishing tools, thus causing damage to the geometry of the workpiece surface and/or the tool.
Co-pending application Ser. No. 966,919, filed Oct. 27, 1992, (abandoned), and 930,116, filed Aug. 14, 1992, (abandoned), disclose a magnetorheological fluid composition, a method of polishing an object using a magnetorheological fluid, and polishing devices which may be used according to the disclosed polishing method. While the method and devices disclosed in that application represent a significant improvement over the prior art, further advances that improve the devices, methods, and results achieved are possible.
This invention is directed to improved devices and methods for polishing objects in a magnetorheological polishing fluid (MP-fluid). More particularly, this invention is directed to a highly accurate method of polishing objects, in a magnetorheological fluid, which may be automatically controlled, and to improved polishing devices. The method of this invention comprises the steps of creating a polishing zone within a magnetorheological fluid; bringing an object to be polished into contact with the polishing zone of the fluid; determining the rate of removal of material from the surface of the object to be polished; calculating the operating parameters, such as magnetic field intensity, dwell time, and spindle velocity, for optimal polishing efficiency; and moving at least one of said object and said fluid with respect to the other according to the operating parameters.
The polishing device comprises an object to be polished, a magnetorheological fluid, which may or may not be contained within a vessel, a means for inducing a magnetic field, and a means for moving at least one of these components with respect to one or more of the other components. The object to be polished is brought into contact with the magnetorheological fluid and the magnetorheological fluid, the means for inducing a magnetic field, and/or the object to be polished are put into motion, thereby allowing all facets of the object to be exposed to the magnetorheological fluid.
In the method and devices of this invention, the magnetorheological fluid is acted upon by a magnetic field in the region where the fluid contacts the object to be polished. The magnetic field causes the MP-fluid to acquire the characteristics of a plasticized solid whose yield point depends on the magnetic field intensity and the viscosity. The yield point of the fluid is high enough that it forms an effective polishing surface, yet still permits movement of abrasive particles. The effective viscosity and elasticity of the magnetorheological fluid when acted upon by the magnetic field provides resistance to the abrasive particles such that the particles have sufficient force to abrade the workpiece.